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Summary DNA extracted from a chicken lymphoblastoid cell line (MSB-1) originally derived from a Marek's disease tumour was examined for the presence of the Marek's disease virus genome. DNA cRNA membrane filter hybridization experiments established the presence of 60 to 90 genome equivalents in these cells.

Sedimentation analysis and intensity fluctuation spectroscopy have been used in conjunction with the Svedberg equation to determine the particle molecular weights of Rous sarcoma virus (Prague strain) and avian myeloblastosis virus (BAI strain). The molecular weights of these two viruses are (294 ± 20) × 10 6 and (256 ± 18) × 10 6 , respectively. Values for the molecular weight of the RNA contained in each particle have been calculated as (5.58 ± 0.5) × 10 6 and (5.88 ± 0.5) × 10 6 . Since the proportion of the viral RNA represented by 4 to 7 S low-molecular-weight material is known, the molecular weight of the 60 to 70 S genomes may be calculated to lie in the range (3.8 ± 0.3 to 4.8 ± 0.4) × 10 6 for both particles. These estimates for the molecular weight of the 60 to 70 S genome are much lower than previous estimates and fall within the range of current estimates of the size of a single 35 S subunit. The implications of this finding are discussed in terms of current theories for the structure of the genome of RNA tumor viruses.

Subcloning of Simian virus 40 (SV40) T antigen-positive mouse-human hybrids, derived from the fusion of mouse cells deficient in thymidine kinase with SV40-transformed Lesch Nyhan fibroblasts, resulted in their segregation into T antigen-positive and negative subclones. Positive correlation between the presence of human chromosome 7 and the expression of SV40 T antigen was established in the subclones examined. These results negate the possibility of a transfer of the SV40 genome to a mouse chromosome.

A set of 64 mutants of Saccharomyces cerevisiae that confer sensitivity to X-ray inactivation were analyzed genetically to determine the number of genetic loci involved. The mode of interaction of various combinations of mutants was also determined. A minimum of 17 genes, when mutant, increase X-ray sensitivity of yeast, primarily by eliminating the resistance of budding haploid cells and by removing the shoulder on the survival curves of diploid cells. Eight mutant loci affect principally X-ray sensitivity while the remaining genes also control sensitivity to ultraviolet. Some of the genes when homozygous block sporulation or result in partial or complete sterility. Examination of the survival responses of multiple-mutant strains indicated a minimum of two pathways in the repair of X-ray damage. A number of the mutants have been mapped and these were found to be dispersed over the genome.

Genetic crosses were made using strains of Saccharomyces cerevisiae which carried cytoplasmically inherited markers conferring resistance to erythromycin, oligomycin and chloramphenicol. The frequency of transmission of these mitochondrial loci to diploid progeny was found to be influenced by the physiological state of the haploid parents, and was not affected by the cis or trans configuration of the three resistance markers. No recombinational polarity was seen in any of the crosses. Growth of a haploid parental strain to stationary phase in a yeast extract peptone medium containing glycerol as a carbon source resulted in a high level of transmission of mitochondrial markers when crossed with a strain grown to stationary phase in the same medium but with glucose as carbon source. When cells were grown under the same conditions as those used in the genetic crosses they were found to contain more mitochondrial DNA relative to nuclear DNA when glycerol was used as a carbon source than when glucose was used. Two criteria were used to determine the amount of mitochondrial DNA present: i) incorporation of radioactive precursors into the different DNA species; and ii) measurement of the mass of DNA from amounts of ultraviolet-absorbing material at the appropriate buoyant densities in isopycnic CsCl gradients. It is proposed that the two to three fold difference in the ratio of mitochondrial DNA to nuclear DNA in stationary phase cells grown in the presence of glycerol compared to glucose reflects an increased number of mitochondrial genomes in derepressed mitochondria. This difference, by a “genome dosage” effect, could account for the variations in the genetic parameter of the frequency of transmission, i.e., strains grown with glycerol as a carbon source contain more mitochondrial genomes than glucose-grown strains and thus will contribute more mitochondrial markers to the zygote.

True F1 hybrid between diploid O. punctata and Ceylonese officinaJis (CC) was first produ-ced by the authors. The F1 hybrids within diploid O. punctata showed complete pairing in chromosomes at MI, while those between diploid O. punctata and the others (intermediate form, O. eichin-geri and Ceylonese officinalis) showed low pair-ing in mean at MI, various irregularities and complete sterility of seed. Based on the present results and other evi-dences, the authors again Propose that the genome of diploid O.punctata should be des-ignated as BB.

This paper points out certain theoretical problems in DNA synthesis associated with antiprimer transcription and with circularization that could oblige RNA tumor viruses to rely on a polyploid genome. It is suggested that each completed act of reverse transcription may be coupled with an act of genetic recombination aimed at recovering the antiprimer information from an adjacent genome subunit in a polyploid train. A partially double-stranded DNA transcript could then be formed with sufficient terminal redundancy to permit circularization. The model provides satisfactory explanations for observed genetic interactions (particularly recombination and heterozygote formation), for inactivation data and for selective subunit transcription.

Ethidium bromide, an inhibitor of mitochondrial transcription, inhibits phosphate uptake, valine incorporation, and uridine incorporation in fertilized eggs of Strongylocentrotus purpuratus, the purple sea urchin. Phosphate uptake, valine incorporation, and valine influx are also inhibited by this drug in artificially activated nucleate and anucleate egg fragments. Ethidium bromide does not affect the egg respiration and it has no measurable effect on ATP level and labeling. It is concluded that the post-fertilization appearance of the phosphate-carrier system does not require the participation of the nuclear genome but that of the mitochondrial one. It is likely that the same proposal holds for the L-valine-transport system. Some effects of ethidium bromide on development are exposed.

Phage P22 is known to have a linear duplex chromosome which is circularly permuted and terminally repeated. The propagation of these features of the mature phage DNA is accounted for by the fact that phage DNA lengths (headfuls) are cut from an intracellular intermediate form of phage DNA several phage genomes in length (concatemer) as first suggested by Streisinger. Studies with mutant phages show that cutting of concatemer DNA is intimately connected to the morphogenesis of the phage head. We have also found, by constructing a partial denaturation map of mature P22 DNA, that circular permutation in P22 DNA is restricted: all of the ends of the mature DNA fall within 20% of each other on the physical map. The limited distribution of ends can be explained by Streisinger's “headful” packaging model with the additional specifications that: a. the intracellular precursor DNA is no longer than ten times the length of mature phage DNA; b. encapsulation of DNA starts at a unique site; c. encapsulation proceeds sequentially therefrom. This model is supported by the distribution of molecular ends in denaturation maps of two deletion phage DNAs. We found, as expected from our model, that the extent of permutation is a direct function of the length of terminal repetition.

The level of redundancy of ribosomal genes, and the relationship of this level to nucleolar formation at different stages of embryonic development, have been examined in the Mexican axolotl, Ambystoma mexicanum. Individuals from 4 inbred stocks were examined, as well as descendants from 2 nucleolar variants which, in the heterozygous condition, are distinguished by exceptionally small nucleoli. Ribosomal RNA-DNA hybridization assays show that one of the 4 wild type lines has only about one-third as much ribosomal DNA (rDNA) as the other three. One of the nucleolar variants has the same level of rDNA as the larger wild-type level; the other variant has the same amount as the smaller ribosomal genome line. Both original nucleolar variants arose as F1 progeny of crosses between a large rDNA genome line and the small genome line. Cytological examination of pregastrula stage embryos from wild type and nucleolar variant lines show that the lengths of the nucleolar organizer regions (NOR) and the sizes of nucleoli formed, are directly correlated with the amount of rDNA present at the nucleolar locus. During gastrulation of the nucleolar variants, however, a transition appears to take place and the amount of rDNA ceases to be the determining factor in nucleolar size. After late gastrula, heterozygous progeny resulting from crosses of either large rDNA genome or small rDNA genome wild type individuals with either nucleolar variant line, have a small and a large nucleolus. The factor or factors associated with this apparent lack of competitive ability of the variant NOR, when opposed to a normal NOR, are unknown. It might be suggested that since the chromosomal alterations which produced the nucleolar variants in both cases eliminated the gene determining the dark colour pattern, they could at the same time have eliminated other genetic material.

Summary The simple sequences of Drosophila melanogaster DNA have been investigated after an extensive fractionation of the genome by actinomycin-CsCl and Ag + - Cs 2 SO 4 preparative gradients. In addition to the simple sequence satellites which occur in lengths with molecular weights greater than 10 million daltons, further evidence is presented for the existence of simple sequences of molecular weight less than 10 million daltons which are associated with less rapidly renaturing DNA. This pattern is a property of only a small number of the DNA fractions at 9.5 million daltons. It is not a generalized feature of the main band DNA sequences which are believed to be genetically active. Thus, the simple sequences investigated here represent a class different from that studied by Wu and Bonner [16, 17] which has slower renaturation kinetics and uniform distribution throughout the genetically active genome as 150 base pair long stretches of middle repetitive DNA spacing unique DNA sequences about 750 base pairs in length. The data presented here are consistent with the existence of a special class of non-satellite simple sequence DNA amounting to more than 10 p. cent of the genome and being associated with less redundant DNA sequences at 10 7 daltons, as proposed by Kram et al. [ 6 ].

The chromosomal proteins of two rapidly growing and poorly differentiated Morris hepatomas were compared with those of liver from normal and tumor bearing animals. While the total quantity of histone associated with DNA in all tumor and liver chromatin preparations studied were similar, tumor chromatin contained an increased quantity of nonhistone chromosomal proteins. Variations in specific classes of histones and nonhistone chromosomal proteins associated with the genome of the two tumors, host liver and liver of tumor bearing animals were observed.

The complexity of Rous sarcoma virus RNA has been determined using molecular hybridization. Relative to poliovirus RNA, the complexity of Rous sarcoma virus is 9·3 × 10 6 daltons, a value close to its physically-determined molecular weight of about 10 7 . Our interpretation is that the 35 S RNA subunits of the 70 S virus genome are non-repetitive, that is, each possesses a unique nucleotide sequence, although a limited amount of redundancy cannot be excluded.

Polyacrylamide-slab gel electrophoresis showed that the nature of peroxidases in wheat is a genetic character; different genomes control the synthesis of specific peroxidases. The growing conditions have no influence on isozyme patterns. Within a single species the electrophoretic patterns of peroxidases may differ from one variety to another. Thus, two classes of Triticum aestivum can be distinguished. With Triticum durum the dissimilarity of enzymograms is particularly important.

SummaryPlagiochila praemorsa Stephani has a diploid complement of 18 chromosomes, including a dimorphic pair of microchromosomes which constitute an X-Y sex chromosome mechanism. This mechanism differs from the « structural sex chromosome » mechanism described in certain other Plagiochila spp. It is suggested that a difference in the distribution of heterochromatin between male and female plants is more likely to be a consequence of the presence of the male or female genome rather than a sex determining mechanism.

Skin grafts transplanted from B 10.HTT donors onto (A.TL X B 10)F 1 recipients are rapidly rejected despite the fact that the B10.HTT and A.TL strains should be carrying the same H-2 chromosomes and that both the donor and the recipient contain the B10 genome. The rejection is accompanied by a production of cytotoxic antibodies against antigens controlled by the Ir region of the H-2 complex. These unexpected findings are interpreted as evidence for a third histocompatibility locus in the H~ complex, H-2I, located in the Ir region close to H-2K. The B 10.HTT and A.TL strains are postulated to differ at this hypothetical locus, and the difference between the two strains is explained as resulting from a crossing over between the H-2 tl and H-2 s chromosomes in the early history of the B10.HTT strain. The H-2 genotypes of the B10.HTT and A.TL strains are assumed to be H-2KsIrs/kSskH-2D d and H-2KsIrkSskH-2D d, respectively. Thus, the H-2 chromosomes of the two strains differ only in a portion of the Ir region, including the H-2I locus. The B 10.HTT(H-2 tt) and B10.S(7R)(H-2 th) strains differ in a relatively minor histocompatibility locus, possibly residing in the Tla region outside of the H-2 complex.

An attempt was made to transfer the murine sarcoma virus genome from cryptically transformed HT-1 cells to hamster embryo cells via isolated chromosomes (chromosome immigration). Chromosome immigration did not result in any transformation of recipient embryo cells. However, there was transfer of a rescuable sarcoma virus genome. Evidence indicates that the transfer requires the intact chromosome structure. It was not possible to identify one or any chromosome associated with the rescuable sarcoma genome.

Cleavage of simian virus 40 DNA I with the restriction endonuclease from Hemophilus aegyptius yields 16 fragments of approximately 18 to 1520 nucleotides. These fragments have been ordered and precisely aligned with the fragments composing the H. influenzae and H. parainfluenzae endonuclease cleavage maps of SV40 † by a combination of two methods: (1) hybridization of radioactively labeled transcripts of Hae fragments to denatured Hin fragments; (2) reciprocal digestion of Hin fragments with H. aegyptius endonuclease and Hae fragments with the endonucleases from H. influenzae and H. parainfluenzae , followed by size analysis of the resultant products. In addition, nucleic acid hybridizations have been performed between the transcripts of certain Hae fragments and DNA from the adenovirus-SV40 hybrids, Ad2 + ND 1 , Ad2 + ND 4 and E46 + , which permit more precise localization of the distal termini of the SV40 segments within these hybrids on the map of the SV40 genome.

DNA-DNA hybridization experiments among coryneform bacteria from soil, cheese and sea fish were performed and the genome sizes of 60 of these bacteria determined.

Chromosome pairing in the tetraploid F1 hybrid (AAAB) from B. erectus (AAAA) × B. pumpellianus ssp. dicksonii (AABB) was very complete. The pairing in a 61-cell sample from one hybrid plant was 1.97 IV + 0.51 III + 8.43 II + 1.75 I. Three cells containing a pentavalent, hexavalent or an octavalent were also found. The pairing results show that the A genomes of B. erectus and B. pumpellianus ssp. dicksonii are homologous, and that the A and B genomes are nearly homologous with few gross structural changes. Bromus pumpellianus ssp. dicksonii should be considered a segmental allotetraploid with predominant bivalent pairing.

We have reviewed our recent evidence for the following scheme for synthesis and integration of viral DAN after infection of permissive cells by ASV: Within the first 3 hours of infection, duplex, virus-specific DNA the length of a subunit of the viral genome (3 times 10(6) daltons) is synthesized in the cytoplasm of infected cells by a virion-associated DNA polymerase; viral DNA probably forms a covalently closed circular duplex prior to integration into host nuclear DNA. Integration and the usual consequences of viral infection can be inhibited by ethidium bromide. We have described a number of features of viral DNA prior to its integration and have indicated how these features can be exploited in the purification of viral DNA. Viral DNA has also been measured in nonpermissive (mammalian) cells in which the variable expression of viral genes is controlled by unknown mechanisms.

Avena canariensis, a recently discovered oat species from Fuerteventura in the Canary Islands, has distinctive ecotypes, is polymorphic in morphological traits and in protein and esterase patterns forming clinal areas within the elevation gradient on the island. A comparison of leaf esterase patterns with that of other species provides evidence favoring A. canariensis as donor of the A genome in the A. magna–A. murphyi–A. sterilis evolutionary cluster.

Although the diploid species Avena canariensis has a number of morphological features in common with the hexaploid species of Avena, the degree of chromosome pairing in the tetraploid hybrid A. canariensis × A. sativa did not reveal closer homology with A. sativa than that of another diploid species, A. prostrata. The chromosomes of both these newly described diploid species are only partially homologous with one of the genomes of A. sativa. The two diploid species A. prostrata and A. canariensis are differentiated by translocations involving three pairs of chromosomes.

DNA was synthesized with detergent-disrupted virions of several C-type viruses and used to measure the extent of homology among the genomes of these viruses by molecular hybridization. The DNA was reacted with viral RNA under conditions which permit saturation of most if not all complementary nucleotide sequences in the RNA. This technique provides a quantitative estimate of the extent of homology among viral RNAs and is superior to current procedures that measure the fraction of DNA hybridized to an excess of viral RNA. The genomes of RD-114 and Crandell virus are at least 85% related, whereas there is no detectable homology among the genomes of RD-114 virus, feline sarcoma-leukemia viruses, murine leukemia virus, avian sarcoma virus, and visna virus. The genome of feline sarcoma-leukemia viruses, like that of RD-114 virus, is at least partly homologous to DNA from normal cats, suggesting that normal cats harbor endogenous genes coding for components of at least two classes of C-type viruses.

Explanted mouse blastocysts were microinjected in the blastocoel cavity with simian virus 40 (SV40) viral DNA. After surgical transfer to the uteri of pseudopregnant surrogate mothers, approximately 40% of the blastocysts developed to term and became healthy adults without apparent tumors at 1 year of age. Molecular hybridization tests for the presence of SV40-specific DNA sequences were conducted on DNA extracted from various organs of these animals. Between 0.5 and 13 SV40 genome equivalents per diploid mouse DNA value were found in some organs of approximately 40% of the adult survivors; this represents a substantial augmentation of the amount administered per embryo. The results are consistent with the working hypothesis that the SV40 DNA may have been integrated into the host genome; alternatively, the viral DNA may have replicated as an extrachromosomal entity or by lytic infection in a few permissive cells. Persistence of the viral DNA from preimplantation stages to adult life may thus provide a new tool for experimental investigation of vertical transmission and expression of tumor viruses.

A genetic analysis was made of two lines which when subjected to disruptive selection with compulsary mating of opposite extremes (D−) showed a different response viz. one, D−-1, showing predominantly an increase of environmental variance and possibly interaction variance, the other, D−-2, showing an increase of genetic variance. Crosses between extreme flies within lines revealed that D−-1 genomes from large flies are dominant to genomes from small individuals. In D−-2 the genetic variation is predominantly additive variance. Tests for dominant chromosome effect in crosses with an inbred stock with recessive markers showed clear third chromosome differences in D−-2 and not in D−-1. Chromosome exchange between extreme flies corroborated the importance of genetic differences in D−-2. A factor or complex of factors with large effect decreasing body size is located on third chromosomes from small flies in D−-2. Interaction between chromosomes has a similar magnitude in the two lines. Crowding and temperature experiments did not reveal an increased general sensitivity to environmental factors in D−-1, which was suggested by the enlarged environmental variance of this line.

Digestion of mouse L cell mitochondrial DNA with Eco RI restriction endonuclease produces two linear duplex fragments comprising 86.3 ± 2.0% and 14.2 ± 1.0% of the circular genome length (16,000 ± 470 nucleotide pairs). Digestion of human HeLa cell mitochondrial DNA with Eco RI produces three linear duplex fragments comprising 49.2 ± 1.0%, 44.4 ± 0.9%, and 6.4 ± 0.4% of the circular genome length (16,590 ± 710 nucleotide pairs). These fragments are shown to be generated by cleavage in unique regions of the mouse and human mitochondrial DNAs. An electron microscopic analysis of partially replicated molecules cleaved by Eco RI establishes a unidirectional mode of DNA replication for L cell mitochondrial DNA. The origin for DNA replication is located on the larger Eco RI fragment at a position that is 1,890 ± 250 nucleotide pairs (11.8 ± 1.2% of the circular genome length) from the proximal restriction site. Replication proceeds unidirectionally away from this restriction site throughout the length of the larger Eco RI fragment. Analysis of L cell, D-loop mitochondrial DNA cleaved by Eco RI indicates that a unique sequence is synthesized in formation of the D-loop in these nonreplicating molecules. The origin of D-loop synthesis is located on the larger Eco RI fragment at a position 1,760 ± 180 nucleotide pairs (11.0 ± 1.1% of the circular genome length) from the proximal restriction site and is, therefore, the origin for unidirectional displacement replication.

Large heritable differences in plant weight and in nuclear DNA amount can be induced in certain varieties of flax. The difference in DNA between the two stable types has been examined by analytical ultracentrifugation, thermal denaturation and renaturation kinetics. No differences in any localised nucleotide sequences are detectable by these methods. It is concluded, therefore, that the additional DNA found in L is representative of a wide spectrum of the flax genome in terms of composition, repetition and complexity of nucleotide sequences.

The germ line and somatic mutation theories of antibody diversity inadequately explain some recent structural and genetic data. The “episomal” insertion theory or some modification of it, seems more consistent with contemporary observations that suggest that immunoglobulin variable regions contain information encoded in separate portions of the genome. The model proposes that at least three groups of genes control the synthesis of a single polypeptide chain. Thegroup one genes code for the relatively invariant portions of the variable region and are few in number (perhaps one per subgroup). A larger number ofgroup two genes encode the hypervariable regions, while a small number ofgroup three genes encode the constant regions. A “copy choice” mechanism is favored for the gene interaction necessary for the synthesis of a single polypeptide chain.

Restriction endonucleases isolated from Hemophilus influenzae, Hemophilus parainfluenzae , and Hemophilus aegyptius were used to cleave ϕX174 replicative form DNA into three sets of specific DNA fragments. The order of these fragments in the ϕX replicative form molecule was determined by ( 1 ) analysis of partial digest products, ( 2 ) analysis of overlapping sets of fragments produced by two different restrictive enzymes. On the basis of these results, a detailed physical map of the ϕX174 genome has been constructed with respect to the cleavage sites of all three enzymes.

— A rapid assay for DNA photolyase was developed that makes use of the membrane binding technique of A. D. Riggs, H. Suzuki and S. Bourgeois, J. Mol. Biol.48, 67–83 (1970). The complex formed between UV-irradiated bacteriophage T7 DNA-3H and the enzyme is trapped on a nitrocellulose filter after a five-minute equilibration and is counted. Using this technique, one can calculate the molar concentration of enzyme in an enzyme preparation and the saturation constant (K) for the complex formation. The latter value is 2.6 cyclobutadipyrimidines per genome (T7) for yeast DNA photolyase; thus approximately 5.2 dipyrimidines/genome are necessary for the full retention of the DNA on the membrane. The speed and reproducibility of the new method makes it a convenient one for assaying column effluents and as many as one hundred samples can be handled routinely in an afternoon.

Stable λN − c I − lysogens contain 20–25 copies of the λ genome per bacterial genome. Less than 10% of the λ genomes occur as closed circular plasmids. The remaining λ genomes can not be separated from the bacterial DNA by centrifugation in neutral sucrose. We suggest that the bacterial chromosome contains several tandemly integrated prophages which replicate at a higher rate than the remainder of the chromosome.

Resistance of simian virus 40 (SV40) DNA to cleavage by Hemophilus parainfluenzae II ( Hpa II) restriction endonuclease has been used as a positive, in vitro selection for mutants lacking the one Hpa II endonuclease-cleavage site of wild-type SV40 DNA. Each of 10 viable mutants isolated by this procedure multiplies significantly more slowly than wild-type virus and contains a small deletion (80 to 190 base pairs in size) of the region of the genome that includes the Hpa II endonuclease-recognition sequence. These well-defined mutants, having a selective disadvantage for growth, would not have been readily obtained by conventional methods used to screen for viral mutants. Therefore, in certain circumstances, restriction endonucleases are effective reagents for the selection of new classes of mutants. Because these small deletions can be visualized in heteroduplexes, these mutants provide internal markers for mapping other alterations or features of the simian virus 40 genome.

DNA-RNA hybridization studies between 70 S RNA from avian myeloblastosis virus (AMV) and an excess of DNA from (i) AMV-induced leukemic chicken myeloblasts or (ii) a mixture of normal and of congenitally infected K-137 chicken embryos producing avian leukosis viruses revealed the presence of fast- and slow-hybridizing virus-specific DNA sequences. However, the leukemic cells contained twice the level of AMV-specific DNA sequences observed in normal chicken embryonic cells. The fast-reacting sequences were two to three times more numerous in leukemic DNA than in DNA from the mixed embryos. The slow-reacting sequences had a reiteration frequency of approximately 9 and 6, in the two respective systems. Both the fast- and the slow-reacting DNA sequences in leukemic cells exhibited a higher T m (2 C) than the respective DNA sequences in normal cells. In normal and leukemic cells the slow hybrid sequences appeared to have a T m which was 2 C higher than that of the fast hybrid sequences. Individual non-virus-producing chicken embryos, either group-specific antigen positive or negative, contained 40 to 100 copies of the fast sequences and 2 to 6 copies of the slowly hybridizing sequences per cell genome. Normal rat cells did not contain DNA that hybridized with AMV RNA, whereas non-virus-producing rat cells transformed by B-77 avian sarcoma virus contained only the slowly reacting sequences. The results demonstrate that leukemic cells transformed by AMV contain new AMV-specific DNA sequences which were not present before infection.

Genome relationships between the three diploid oats, Avena strigosa (S.), A. longiglumis (L.) and A. prostrata (P.) were studied by chromosome pairing in diploid hybrids and in synthetic triploids and tetraploids combining these genomes. Fairly regular pairing in the diploid hybrid and typical autopolyploid behavior in the triploids and in the amphidiploid suggest small differentiation in the chromosome architecture of A. longiglumis and A. prostrata. A. strigosa diverges from the other two oats by complex chromosome rearrangements. Conspicuous preferential pairing took place in triploids with SSL, SSP and SPP genomic constitution. The low bivalent frequency in the SLL triploid suggests that preferential pairing in triploids with two S genomes is not a consequence of chromosome rearrangement but is rather of genetic origin. The presence of the three genomes in a triploid or a tetraploid caused considerable meiotic irregularities suggesting a better pairing competition of the S genome.

Prefractionation of chromosomal proteins in 5 m urea with stepwise increase in NaCl molarity has been used to facilitate the examination of nonhistone chromosomal proteins isolated from various rabbit tissues. Electrophoretic analysis on polyacrylamide gels under denaturing conditions of the protein fractions derived from brain, liver, heart, and submandibular salivary gland chromatins displays reproducible compositional differences in nonhistone chromosomal proteins. The enzymatic removal of 48% of protein-bound phosphate with alkaline phosphatase does not significantly alter the electrophoretic mobility of these proteins. With the present technique, it is estimated that chromatin polypeptides (of average M r 100,000) occurring in greater than 3 × 10 4 copies per genome can be detected. At this level of sensitivity, a significant fraction of total nonhistone chromosomal proteins manifests organ specificity.

On the basis of the chromosome behavior of a backcross between a colchicine-induced amphiploid (6x) from a cross between Hordeum jubatum L. and H. compressum Griseb. and H. jubatum (4x), the following genome relationship between H. jubatum, H. compressum and closely related species is suggested: H. jubatum, AAA′A′, H. brachyantherum, A A A′A′, H. californicum, A A, and H. compressum, A′A′. Also, an argument is proposed for genetic control of chromosome pairing.

From previous studies, lymphocyte DNA from human leukemias and DNA from involved tissues of patients with Hodgkin's disease or Burkitt's lymphoma contain sequences that are absent from their normal counterparts. These sequences are related to those found in particulate elements associated with these neoplasias and possessing biochemical properties characteristic of RNA tumor viruses. Similar observations have been made of unique sequences related to those of the feline virus RD-114 and found in spontaneous mastocytomas in cats. Here we extend these results to the classical murine model of virus-induced leukemias. Splenic DNA from BALB/c mice with leukemia induced by Rauscher leukemia virus (RLV) possess some RLV-related sequences that do not exist in normal BALB/c DNA. Furthermore, these leukemia-specific sequences were absent in all other mouse strains examined, including AKR, a strain with a high incidence of spontaneous leukemia. The DNA of all noninfected mouse strains possesses considerable homology with the RLV genome. Temperature denaturation studies indicate, however, that although the RLV-related sequences found in all normal mice are similar to each other, they are not exactly homologous with RLV sequences. We conclude that RLV-induced leukemia in BALB/c results in the insertion of RLV sequences into cellular DNA that itself possesses only partial homology with the RLV genome.

Nuclear DNA content of Ae. squarrosa, natural Emmer and natural and synthesized Dinkel wheats, in addition to Tetra Canthatch (AABB) which was extracted from common wheat, was measured Feulgen-microspectrophotometrically using PMC's at first prophase or pollen tetrads.A significant amount of variation in DNA content per nucleus was observed among seven strains of Ae. squarrosa, indicating intraspecific differentiation accompanied by gain or loss of genetic material in this diploid species.DNA content per nucleus of the extracted tetraploid (Tetra Canthatch) was the same as those of present-day natural Emmer wheat; no appreciable quantitative change in nuclear DNA of the A and B genomes of common wheat seems to have taken place during at least the past seven thousand years, in spite of considerable genetic changes that have occurred.Two natural and six synthesized hexaploids had similar DNA content that was approximately equal to the sum of those of their parents.Evidence concerning variation in nuclear DNA content of higher plants was reviewed and quantitative relationships between diploid and polyploid species in DNA content was discussed in relation to its evolutionary significance.

The ascending genome size in Gossypium is assumed to be D, A, B, E and F, and C. Feulgen cytophotometry revealed that mean value of DNA content for each genome was D= 10.95, B = 13.88, F = 14.31, E = 18.24, A = 18.66, and C = 20.30, and that there is a close relationship of genomic chromosome size and DNA content. Evidence suggests that the five genomes with large chromosomes arose from a D genome-like progenetor by large scale, saltatory replication of repetitive DNA distributed uniformly through the ancestral genome. Corresponding adjustment in recombination units did not accompany the two-fold divergence in DNA value of the two homoeologous A and D genomes in the allotetraploid species.

Temperature-sensitive mutants of the adenovirus 2-simian virus 40 hybrid, Ad2+ ND1‡, were isolated and crossed with temperature-sensitive mutants of adenovirus type 5 (Ad5). Forty-five wild type recombinants were selected and their DNAs were separately digested with five restriction endonucleases, EcoRI, HpaI, BamI, HindIII and SmaI. There are 15 sites cleaved by these enzymes that are unique to one parental DNA or the other. The fragments obtained by digestion of each of the recombinant DNAs were separated by gel electrophoresis and compared with those obtained from the parental genomes. The recombinant DNAs were found to consist of sequences derived both from Ad5 and from Ad2+ND1. Knowing the positions at which the five restriction enzymes cleave the genomes of the parental serotypes, it was possible to decide which regions of each recombinant DNA are composed of Ad5 and which of Ad2+ND1 sequences. In this way the cross-over events that generated the recombinants were mapped and the physical locations of the ts mutations in the parental genomes were determined.

Five clonal isolates of purified polyoma defective DNA [Fried, M. (1974) J. Virol. 13, 939-946] have been examined by electron microscopy. Four isolates (D-92, D-74, D-50, and D-47) are largely homogeneous in sequence, whereas, the fifth isolate (D-80) is somewhat heterogeneous. Polyoma nondefective DNA is cleaved in a unique region of the genome by the EcoR I endonuclease. Hybridization of the resulting linear molecules with randomly nicked defective DNA reveals distinguishable types of heteroduplex structures for each of the different defective DNAs. Although the defective DNAs are shorter than polyoma nondefective DNA, the heteroduplex experiments demonstrate that they are not simply deletion mutants containing only a portion of the viral genome. Three isolates (D-92, D-50, and D-47) contain regions of homology to polyoma DNA covalently linked to non-homologous regions. One isolate (D-74) contained no regions of detectable homology to polyoma DNA. Another isolate (D-80) contained a large proportion of molecules with duplicated-inverted regions. Some of these isolates of defective DNA may contain specific host sequences at the site(s) of integration of the polyoma genome during the lytic cycle in mouse cells. A process we term “abortive replication” may explain the formation of different types of defective DNAs.

Maize stocks with or without additional heterochromatin (a B chromosome or abnormal chromosome 10), and a stock heteromorphic for a reciprocal translocation, were used in a study of homologue synchrony of replication. Batches of attached primary roots were pulse labelled with 3H-TdR and sampled at hourly intervals during the S period (at 18° C). Silver grain counts over each chromosome arm from 25 cells at each collection period were submitted to analyses. Qualitative synchrony (concordance) was tested between chromosome arms using a χ2 test. Quantitative synchrony was tested with an I-divergence test. Results from these tests in the control experiments were consistent with the hypothesis of meta-synchrony of homologue replication. The addition of heterochromatin in the form of a B chromosome or an abnormal 10 chromosome increased asynchrony two-fold. The insertion of a heteromorphic translocation into the genome produced a similar though less pronounced effect.

We characterized defective DNA molecules of large-plaque and small-plaque SV40 produced and accumulated during serial undiluted passages. The electron microscope heteroduplex method revealed that defective SV40 DNA contains deletions, insertions and substitutions. The majority of the large-plaque defective molecules had a simple deletion. The deletions were heterogeneous in size, and the sites of deletion appeared to be mostly overlapping. The majority of the small-plaque defective molecules had a deletion, and more than half of the deletion molecules also had an insertion at a separate site. The small-plaque SV40 genome appeared to have more sites for deletion to occur than large-plaque SV40, and the deletions have occurred at more than two sites. The change of a local nucleo tide sequence resulting from mutation may be related to the difference between the two plaque types.

DNA was isolated from three species of bees: the common honey-bee ( Apis mellifera ), the Indian honey-bee ( Apis cerana ), and the leaf-cutting bee ( Megachile rotundata ). The guanine-cytosine distribution of the two honey-bee DNAs is relatively broad and skewed toward lower values; leaf-cutting bee DNA shows a narrow distribution. No distinct satellite bands are present in any of the species. Renaturation kinetics indicate that the genome sizes of the two honey-bee species are identical to one another and somewhat smaller than that of the leaf-cutting bee. About 89 per cent of the genome of all three species renatures slowly; this fraction presumably comprises the single-copy (unique) sequence portion of the genome. Sufficient DNA was isolated from the dwarf honey-bee ( Apis florea ) to determine a guanine-cytosine distribution. Like the other honey-bee species, the distribution is relatively broad.